Hello Everyone,

Let me explain my project before i ask the all important question/
Currently we have around 80 signals(40 analog signals and 40 digital signals) going from the control hardware to a master PLC.
To optimize the complete hardware,I am planning to convert these signals to be transmitted digitally.
The distance between the PLC and the control hardware is about 5 meters
The cycle time of the PLC is 20 ms.The PLC can accept signals via profibus or ethernet.

Which protocol is better suited for this operation?

 

Morning,

I would imagine it depends on implementation.

Profi is RS485, so you are looking at a daisy chain, which can make things complicated. TCP/IP its a star topology, so the physical location of each PLC is less relevant.

Code / HW wise, I figure that most PLCs would either have RS485 built in already, or the module is easy to obtain. TCP/IP, higher level protocol, so I suppose it may be more difficult / expensive to implement. You can implement profibus on ethernet . . . its not restricted to the RS485 bus.

On the other hand, recently consulted on a project where a client wanted their RS485 implementation upgraded to cater to TCP/IP but this was using MCUs and not PLCs. Reason being was the versatility that the TCP/IP offered.

My 2 cents

Michael

 

Morning,

I would imagine it depends on implementation.

Profi is RS485, so you are looking at a daisy chain, which can make things complicated. TCP/IP its a star topology, so the physical location of each PLC is less relevant.

Code / HW wise, I figure that most PLCs would either have RS485 built in already, or the module is easy to obtain. TCP/IP, higher level protocol, so I suppose it may be more difficult / expensive to implement. You can implement profibus on ethernet . . . its not restricted to the RS485 bus.

On the other hand, recently consulted on a project where a client wanted their RS485 implementation upgraded to cater to TCP/IP but this was using MCUs and not PLCs. Reason being was the versatility that the TCP/IP offered.

My 2 cents

Michael

Thanks for your reply, i dont plan to write any drivers for either profi or ethernet, that will be too complicated.I plan to use ready made modules like the WIZ550io, if i am going for ethernet.Simillarly there are many profibus modules also avalable.My main priority here is the time and repeatbility of the protocols.
The master PLC is required to update data every 20 ms, so i dont want any delay more than 20ms during data transmission from my control hardware to PLC.Which protocol out of these two can gaurentee the above for me?

Thanks,
AK

 

The profibus is standardised but the top layers are vendor dependent and could not be always compatible with other systems.
PROFIBUS was defined in 1991/1993 in DIN 19245, was then included in EN 50170 in 1996 and, since 1999, established in IEC 61158/IEC 61784.
If you do not want to program you should buy converters/ interfaces from a supplier compatible with your existing system.
Picbuster